1. Field of the Invention
The present invention relates to a shuttle type of a scanner, and more particularly to a method and apparatus for correcting scanning errors in a shuttle type of a scanner, in which errors for decline of pattern data are detected and corrected and errors for distance between bands are detected so that a carrying distance of a document is corrected.
2. Description of the Related Art
Generally, a shuttle type of a scanner is an apparatus including a scanning head which is reciprocally mounted on a guide shaft disposed normally to a direction of carrying the document and scans an image recorded on the document. The scanner further includes a lamp assembly including a lamp emitting light on the image of the document, a lens assembly including a lens collecting the light reflected from the document, a charge coupled device assembly including a charge coupled device which converts the reflected light collected by the lens into an electric signal. The lens assembly includes a filter and a lens holder which is movable between the charge coupled device assembly and the lamp assembly. The lens assembly and the charge coupled device assembly are rotatably integrated with each other.
A control screw has a thread portion which has thread on the surface thereof to rotate the charge coupled device. On the other hand, the charge coupled device assembly also has a thread formed on the surface thereof which the thread portion contacts. The thread of the control screw is engaged with the thread of the charge coupled device so that the charge coupled device is rotated as the control screw is controlled.
The shuttle type scanner scans a plurality of slices respectively including numbers of pixels simultaneously or in sequence. Provided that a slice includes one hundred sixty pixels, for example, the slice has a size of 13.547 mm (4.67 xcexcmxc3x97one hundred sixty pixels)in a resolution of 300 dpi. That is, a slice of pixels includes the one hundred sixty pixels and a band (referred to as a scanning area which the scanning head scans) includes twenty four hundred slices and twenty two bands are presented in the document having an A4 size.
When the scanner starts to scan the document, scanned data are sequentially stored in a memory a slice by a slice. Therefore, when the scanning of a band of data is completed, the image data having 160xc3x972400 bytes are stored in the memory.
The scanning head does not occasionally align with the document due to a tolerance of a scanning module in assembling the scanner. In this case, the data stored in the memory are discontinued at a boundary of the bands and declined.
Also, the document must be carried by a band but is not accurately carried due to a mechanical tolerance of an electric motor for carrying the document. Accordingly, errors for distance at which the document is carried are generated. As a result, the document is carried at a distance less or more than a band. The data stored in the memory are discontinued at the boundary of the bands and pixels at the boundary of the bands are eccentric to each other.
A worker must adjust the scanning head by handling the control screw to correct errors for decline of the scanning head. The errors for distance of the bands, however, are ignored.
When the worker adjusts the scanning head by handling the control screw to correct errors for decline of the image data, there is a problem in that it is difficult to adjust the scanning head accurately. Furthermore, there is a disadvantage in that since the separate control screw and control zig are required for correcting the errors for decline of the image data, manufacturing of the scanner is complex and productivity for manufacturing the scanner is degraded.
Furthermore, since the errors for distance of the bands are ignored, the quality of printing is degraded.
U.S. Pat. No. 5,644,344 to Haselby, entitled Optical Print Cartridge Alignment System and discloses an apparatus and techniques for aligning the operation of the ink jet printhead cartridges of a multiple printhead ink jet swath printer that includes a print carriage that is movable along a horizontal carriage scan axis, first and second ink jet printhead cartridges supported by the movable carriage for printing onto a print media that is selectively movable along a vertical media scan axis, and an optical sensor supported by the movable carriage.
U.S. Pat. No. 5,250,956 to Haselby et al., entitled Print Cartridge Bidirectional Alignment
In Carriage Axis, disclose an apparatus and techniques for aligning the operation of the ink jet printheads of a multiple printhead ink jet swath printer, and particularly for aligning the operation of the printheads along the carriage scan axis. The patent discloses the relative positions of vertical test line segments printed by the cartridges at a fixed swath position are determined with an optical sensor. The relative position information is disclosed as being utilized to calculate horizontal alignment corrections for the printhead cartridges which are utilized to adjust the horizontal offset shifts provided for the swath data and to adjust the timing of the firing of the ink jet nozzles of the printhead cartridges.
U.S. Pat. No. 5,297,017 to Haselby et al., entitled Print Cartridge Alignment In Paper Axis, disclose an apparatus and techniques for aligning the operation of the ink jet printhead cartridges of a multiple printhead ink jet swath printer that includes a print. carriage that is movable along a horizontal carriage scan axis, first and second ink jet printhead cartridges supported by the movable carriage for printing onto a print media that is selectively movable along a vertical media scan axis, and an optical sensor supported by the movable carriage. It is disclosed that alignment of the operation of the printheads along the media scan axis is performed by determining with the optical sensor the relative positions of horizontal test line segments printed by selected nozzles of the printhead cartridges. The relative position information is utilized to calculate a vertical alignment correction which is implemented by enabling selected ink jet nozzles of the printheads and adjusting the position of one printhead cartridge relative to the other such that the nozzles of the ink jet printheads are properly spaced along the media scan axis.
The present invention has been made to overcome the above described problems of the contemporary practice in the art.
It is an object of the present invention to provide a method for correcting scanning errors in a shuttle type of a scanner, in which errors for decline of pattern data and errors for distance between bands are determined by using a computing program and amount of value for correcting the errors is applied to the pattern data every time when scanning a document, whereby the errors for decline of the pattern data and the errors for distance between the bands can be corrected without use of a separate element.
To accomplish the above objects of the present invention, according to one aspect of the present invention, there is provided a method for correcting scanning errors in a shuttle type of a scanner, comprising the steps of: scanning a recordable medium on which pattern data having a straight line shape are recorded in parallel to a direction that a document is carried; detecting scanning errors between an actual coordinate at which the pattern data having the straight line shape are detected in a first line of a first band and an actual coordinate at which the pattern data are detected in a last line of the first band; detecting a first reference point at which a center line of a band intersects the pattern data having the straight line shape in the first band and rotating the pattern data on the first reference point in a direction to the center line by a half value of the scanning errors;
detecting an actual coordinate at which the pattern data having the straight line shape are detected in a second band and determining a presumed coordinate when the pattern data in the second band are extended along the actual coordinate to a last line of the first band; comparing the presumed coordinate with the actual coordinate in the last line of the first band to detect the scanning errors; correcting the scanning errors by moving the pattern data having the straight line shape in the second band by an amount of the scanning errors; and detecting a second reference point at which a center line intersects the pattern data having the straight line shape in the second band and rotating the pattern data having the straight line shape on the second reference point in a direction to the center line by half of the scanning errors, wherein the correcting value for the decline of the pattern data is applied to a document data to correct the scanning errors every time when scanning the document.
The recordable medium can be a pattern sheet and has the straight lines stamped at a point of a frame in a scanning region which is spaced apart from a region on which the document is carried.
According to another aspect of the present invention, there is provided a method for correcting scanning errors in a shuttle type of a scanner, comprising the steps of: scanning a recordable medium on which pattern data having a specified shape are recorded; creating imaginary pattern data by horizontally moving the pattern data having the specified shape by a predetermined number of pixels in a predetermined direction in a first band; detecting an actual coordinate of a pixel in which the pattern data having the specified shape are recorded in a first line of a second band; detecting a contact coordinate at which an imaginary line extending from the actual coordinate in a direction normal to a boundary line between a first band and the second band intersects the imaginary pattern data in the first band; determining scanning errors for a vertical axis between the first band and the second band; horizontally moving the pattern data having the specified shape in a direction opposed to the predetermined direction by a predetermined number of pixels in the first band; detecting a carrying distance of a document by adding an actual carrying distance of the document to the scanning errors for the vertical axis; and storing the carrying distance, wherein the document is carried by the carrying distance every time when scanning the document.
According to a further aspect of the present invention, there is provided a method for correcting scanning errors in a shuttle type of a scanner, comprising the steps of: scanning a recordable medium on which pattern data having an inclined line shape and inclining at an angle of 45xc2x0 are recorded; detecting a first coordinate of a pixel in which the pattern data having the inclined line shape are recorded in a last line of a first band; detecting a second coordinate of a pixel in which the pattern data having the inclined line shape are recorded in a first line of a second band; determining distance errors for a horizontal axis between the first coordinate and the second coordinate; detecting a carrying distance by adding an actual carrying distance of a document to the distance errors for the horizontal axis; and storing the carrying distance, wherein the document is carried by the carrying distance every time when scanning the document.